In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize the features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rate. With this UMTS network, long-term evolution (LTE) has been under study and its specifications have been drafted, for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In a third-generation system, it is possible to achieve a transmission rate of approximately 2 Mbps at the maximum on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in an LTE system, it is possible to achieve a transmission rate of approximately 300 Mbps at the maximum on the downlink and approximately 75 Mbps on the uplink by using a variable band, which ranges from 1.4 MHz to 20 MHz. Also, in the UMTS network, a successor system of the LTE system (referred to as, for example, “LTE-advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) has been under study and its specifications have been drafted, for the purpose of achieving further broadbandization and increased speed.
As duplexing methods in radio communication, there are frequency division duplex (FDD) to divide between the uplink (UL) and the downlink (DL) based on frequency, and time division duplex (TDD) to divide between the uplink and the downlink based on time. In TDD, the same frequency region is applied to uplink and downlink communication, and signals are transmitted and received to and from one transmitting/receiving point by dividing the uplink and the downlink based on time.
In TDD in the LTE system, a plurality of frame configurations (DL/UL configurations) with different transmission ratios between uplink subframes and downlink subframes are defined (see FIG. 1). In the LTE system, as shown in FIG. 1, seven frame configurations, namely DL/UL configurations 0 to 6, are defined, where subframes #0 and #5 are allocated to the downlink, and subframe #2 is allocated to the uplink. Also, generally speaking, in TDD, in one given frequency carrier, the same DL/UL configuration is employed between geographically-neighboring transmission points in order to prevent interference between the transmission points (or the cells).